DESCRIPTION (Applicant's abstract): Analysis of the structure and function of heat shock proteins has led to new insights regarding the pathway of protein maturation. Heat shock proteins, in their role as "molecular chaperones," participate in the synthesis, folding and intracellular transport of many, if not all, polypeptides. Increases in the levels of the heat shock proteins, as occurs in cells experiencing different types of metabolic stress, aid in the renaturation of cellular proteins adversely affected by the stress event and facilitate the synthesis and folding of new proteins needed to replace those which have been irreparably damaged. Herein Dr. Welch will continue to examine structure/function of the heat shock proteins. In first aim the identity and role of molecular chaperones interacting with nascent polypeptides still bound to the ribosome will be pursued. Here the idea that two heat shock proteins, hsp70 and hsp90, together constitute a nascent chain binding complex will be examined. Interaction of this putative nascent chain binding complex with nascent chains is suggested to help stabilize maturing polypeptides, preventing inappropriate intra- or inter-molecular interactions that might lead to misfolding and aggregation. Studies described in aim 2 will serve to complement those in aim 1 by focusing on the maturation of one particular polypeptide, the androgen receptor (AR). The rationale for studying AR biogenesis is 3-fold. First, the biological activities of the mature form of AR are known to require the help of different molecular chaperones. Second, assays to study the proper folding of AR are readily available. Finally and most importantly, mutations in AR are the basis of a neurodegenerative disease. Here expansions of a CAG repeat within the gene encoding AR result in an AR protein containing an unusually long run of glutamine residues. As a result, mutant AR readily forms nuclear and cytoplasmic aggregates which over time lead to cell demise. Thus, in aim 2 Dr. Welch will compare and contrast the maturation pathway of wild type and mutant AR and determine the role served by different molecular chaperones. In parallel, studies described in aim 3 will focus on the cellular impact of mutant AR expression. He proposes that the accumulation of mutant AR-aggregates leads to the sequestration of molecular chaperones and the eventual development of chronic cellular stress. Exactly what metabolic pathways are adversely affected in the cell experiencing chronic stress will be addressed. Finally, in aim 4 we will continue with the identification and characterization of small molecules that are effective in reducing or preventing abnormal protein folding. The principal investigator anticipates that these studies, in sum, will continue to provide new insights regarding the structure/function of the heat shock proteins and their potential role in human diseases involving abnormal protein folding.